There has been known a workpiece bending machine which measures a bending angle of a workpiece bent in cooperation of a punch and a die in the following manner. A cylinder is moved upward from a detector provided on each side of the die in a width direction, so as to bring a predetermined position thereof into contact with a straight part of the workpiece. Simultaneously, a contact, which is provided for the cylinder and biased upward so as to move up and down, is brought into contact with the straight part of the workpiece. A height position of the contact at this time is measured by a length measuring device, and the working piece bending angle is detected from a difference in height and a horizontal distance between the predetermined position and the contact point of the contact. One of the prior technologies relating to the present invention is Japanese Patent Application Laid-open Publication No. 2001-121215 (Patent Literature 1).
In the aforementioned conventional workpiece bending machine, on each side of the die in the width direction on the upper surface of a die holding member (die holder) through which the die is attached to an upper end of a lower table, a guide rail is provided along the longitudinal direction of the die; a slider is provided on the guide rail so as to move in the longitudinal direction of the die; and the detector is provided on the slider. Accordingly, for example, if the guide rail has bad straightness, the detector may move in a rolling manner (for example, the detector moves in a rolling manner, so as to slightly rotate around an axis extending in the direction that the detector moves), thereby sometimes preventing accurate measurement of the workpiece bending angle.
The present invention was made in the light of the aforementioned problem, and an object of the present invention is to provide a workpiece angle detecting device in a bending machine which can measure a workpiece bending angle with high accuracy, the bending machine bending a workpiece in cooperation of upper and lower tools. Another object of the present invention is to provide a workpiece bending angle detecting system and workpiece bending machine including the workpiece angle detecting device.